Base64, URL encoding, and HTML entity escaping solve three different problems that get confused for each other constantly: Base64 turns arbitrary bytes into ASCII text (for embedding binary data in text formats), URL encoding escapes characters that aren't safe in a URL, and HTML entities escape characters that would otherwise be parsed as markup. This handles all three, plus encoding a local file directly to a Base64 data URL.

When you'd use this

Decoding a Base64 API payload or JWT segment to see its actual contents, or encoding a small image into a data URL to embed directly in CSS or HTML without a separate file request.

URL-encoding a query parameter that contains spaces or special characters, or escaping text before inserting it into an HTML template so it doesn't get parsed as markup.

Common errors

"Invalid character" on Base64 decode usually means the input isn't actually Base64 - it's Base64URL (which uses - and _ instead of + and /), or it has line breaks or padding stripped that the decoder needs.

Double-encoding is a common mistake with URL escaping specifically: encoding an already-encoded string turns every % into %25, breaking the original encoding rather than being harmless to repeat.

Frequently asked questions